Shipped ready-to-run
One-stop solution for nitrogen removal

In some projects, teamwork can literally be expressed in units of measurement. Like when you’re building a 900-tonne module. This mammoth component was the result of intense and collaborative development work, overseen by Linde project manager Dr Luis Grimm. He and his team of specialists had to overcome enormous technical and organisational challenges before shipping their nitrogen removal unit (NRU) to its final destination. “We started out with a simple process diagram three years ago,” explains Luis Grimm. “But we knew that we had an extremely complex task ahead of us.” The Linde experts could only achieve their ambitious goal through close collaboration.

Increasing the value of natural gas as a fuel

It all started back in 2013, when Linde Engineering was commissioned to build an NRU for a customer in Western Australia. The unit was to be integrated into one of the country’s largest natural gas plants, where it would be used to increase the calorific value of natural gas so that it could be fed into the local supply grid.

As a one-stop provider, Linde was responsible for the entire process – from planning through the procurement of all parts to module assembly. “Very few companies worldwide can offer a one-stop service for a complex project on this scale,” explains engineering manager Andreas Behrendt. “We have the technical know-how coupled with the engineering and procurement excellence to overcome all the logistical and organisational hurdles involved in a full-service package such as this.”

The project also presented its own cost challenges. Building the unit in Australia would have pushed costs up significantly. As a result, the unit was to be modularised and assembled in Europe. It would then be shipped practically “ready to run” to Australia. Linde decided to assemble the unit in the Spanish port of Tarragona, opting for a modular approach from the get-go. The assembly of the four NRU modules was overseen by the Linde site in Schalchen, Germany.

Process animation of removing nitrogen from natural gas

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The process of removing nitrogen from natural gas

The NRU functions in the following way: The incoming nitrogen-methane mixture is initially pre-cooled to minus 18 degrees Celsius in the first module, the dew point control skid, using plate-fin heat exchangers from Linde. Heavy hydrocarbons are separated through condensation. The nitrogen-methane mixture is then cooled further to minus 186 degrees Celsius in the second module, the coldbox. The components in the mixture can be cryogenically separated in this way because nitrogen and methane condense at different temperatures. The unit vents the nitrogen to the atmosphere while the methane is fed into one of the two pump modules, where it is compressed to different pressures for different applications.

“The coldbox is at the heart of the unit, weighing 350 tonnes and measuring 35 metres,” says Luis Grimm. “It is an extremely complex module and you can’t simply buy it off-the-shelf for an application like this”. The entire unit had to be planned specifically for the conditions in Australia, as Andreas Behrendt explains: “The composition of the natural gas, for example, is different for every project. And it also changes during the lifecycle of the entire unit”. As a result, Linde’s engineers had to factor in a number of different potential scenarios. “Our NRU is designed for different operational conditions. This makes it extremely flexible”.

Nitrogen rejection unit (NRU) model fabrication at Tarragona, Spain

140,000 working hours for assembly

“Coordination was one of the biggest challenges,” adds Grimm. Linde Engineering, however, has decades of experience with complex projects, designing many different unit components and coordinating procurement to ensure each one is available on the construction site – precisely when it is needed. The assembly process was subject to stringent test and safety regulations. In the end, engineers worked 60,000 hours on the project. A further 140,000 hours were needed to assemble the unit in Tarragona.

The customer benefitted from Linde’s all-round package, spanning design, procurement and delivery. “The benefits of a modular design can be summarised in four categories,” explains Ralf Bellaire, Head of Engineering at Linde Engineering. “Number one, reducing construction cost; number two, reducing the construction schedule; number three, minimising the risk exposure; and number four, increasing the quality”.